Even at 5ft 3in, Tom Daley, 14, is easy to spot, hemmed in by TV crews and lunchtime idlers in the sunny environs of the Mall in central London - straight-backed and shining for the cameras like the boy wonder the Olympic people say he is, displaying his dental braces as he turns on his Year 9 grin, an empty Diet Coke bottle dangling from his hand. Tom is doing his bit to help publicise the 2012 Games - or at least the big street party along here at the end of August, as part of the handover hoopla following Beijing. By then Tom, who qualified for the diving squad in February, will have become the second-youngest British male Olympian ever (the dream scenario of being the youngest was dented by the late discovery of a 13-year-old rowing cox from 1960). That seems amazing enough, but people are already asking: can he win a medal? Can he?

The event is winding down here. Boris Johnson has bumbled in and out of the proceedings on his bicycle, and the woman they've hired to dress up as a novelty 2012 windbreak is posing for a few final snaps. Sebastian Coe - momentarily upstaged when President Bush's motorcade came gunning by a few minutes ago, turning heads with its black bulletproof limos and SUVs and outriders, US flags whipping the air - can now be heard telling the BBC why Visa, credit-card giant and event sponsor, is crucial to the national effort.

I say hello to Tom and his dad Rob, and we head across St James's Park for lunch, flanked by two PR minders. Tom seems unruffled by all the recent media attention - hardened against distraction, one imagines, by a life of discipline and competition and foreign travel (he enthuses about his trips to Australia and Mexico - he's got a great tan) and all the other character-building extremes that can turn a boy into a man of the world.

He has already grasped, though, that the more extraordinary life becomes, the more being ordinary appreciates in value. His friends treat him like a normal person, he says - 'which I am, when I'm not diving'; he attends a 'normal' school in Plymouth, which is 'very supportive'; and he and his brothers (Ben, nine, and William, 12) all get on each other's nerves at home, just like normal brothers. Well yes, I say, but he must be abnormally popular with girls! He grins. He has a lot of old friends who are girls, but doesn't get time to meet many new ones, 'but when I can, I do...' He reddens slightly and takes refuge in the menu. 'What are shallots?'

Onions, the PR says. Does he like onions? He likes all vegetables except for mushrooms. Does he like fish cakes? He doesn't like fish, but maybe fish cakes will be OK - if they're not too fishy? His dad doesn't like fish either. He tells us how as a kid he used to hide his fish fingers in his bedroom drawers until his mum smelt them one day and went mad. So, fish cakes then, says the PR. Do you want chips? 'No, new potatoes,' Tom says. 'They're healthier.'

Does he always eat healthy food? 'I can eat what I want but it has to be sensible and balanced - with the occasional treat.'

And his favourite treat? 'Ice cream. I like McFlurry,' says Tom, 'but I am not allowed McDonald's that often. Maybe once every two weeks.'

I lean across to the next table and ask his dad who has the diving genes - him or Mum. Neither, he says. 'There are no sportspeople in the family. It's just hard work. I believe if you take any kid aged five or six and they work at something, you get results.'

Tom says he was swimming from the age of three. He always loved it in the water, then one day at the local pool in Plymouth he saw people diving and he gave it a go. 'The thing is, there were only about four diving pools in the country - Plymouth, Leeds, Sheffield, Manchester - so it was just luck, really. If we'd lived in Birmingham or somewhere, it wouldn't have happened. I started going every Saturday for lessons, then after eight weeks I got a certificate. After that I started doing competitions, training, learning new dives.'

After wiping the floor with everyone at everything in his age group, he entered his first senior competition in 2005. He is currently British champion and European champion on 10-metre platform and on 10-metre platform synchro (with partner Blake Aldridge). He's got a houseful of medals.

'Since qualifying for the Olympics, everything's gone crazy,' he says. 'I wasn't expecting to get into this Olympics at all. But I got into the World Cup top eight in February in Beijing, which preselected me.'

Individually he is ranked seventh in the world, third in the synchronised (his bronze-winning set with Aldridge made him the youngest-ever medallist in a world diving event) - and in 2007 he won the BBC's Young Sports Personality of the Year.

All this requires training - daily three-hour sessions after tea and homework, and two sessions on non-school days. There's trampolining and gymnastics, weights, jumps, conditioning, cardio, stretching, harness work, 'lots of things to build up strength for take-offs' - and that's before he's even got wet.

It sounds like hard work, I say. Aren't there days when he would rather just slob around watching TV or playing computer games? I think of my own four sons, who when it comes to qualifying for the Olympics have thus far proved so disappointing.

'Sometimes you feel you're missing out,' Tom says, 'but you get used to it. And really I don't mind. I'd rather be diving than be at home watching TV, I guess.'

He does get to relax sometimes. He has a Nintendo Wii and likes listening to music on his laptop and seeing his friends or watching films. Does he get lonely away from home? 'I used to get homesick when I was younger - nine or 10. Going away at that age is quite intimidating. But you learn to deal with it.'

He travels with his 'lucky' monkey. And these days his father goes everywhere with him, though the decision to give up work as boss of his own small engineering business was influenced by the alarming news that he had a brain tumour. He's fine now, but Tom was kept in the dark until he'd had the all-clear. Tom says when he qualified for Beijing it was his dad who was in tears, forcing his way past alarmed Chinese security guards to gave him a big bear hug.

I ask about his diving. At senior level he only competes on the high board (the 10-metre platform) - he doesn't have the weight and strength yet for springboard (the three-metre springboard is the only other board used at this level). Even on the platform, his range of complexity is restricted by how high he can jump. 'You get more points for a hard dive done well. But my tariff [degree of difficulty] is lower than the older guys' because they can jump higher. But there is more chance of a hard dive going wrong. If you stick to the easier dive, you've got more chance of doing it well...'

And that's how he keeps winning - with easier dives done better? 'Well, there's a kind of luck as well. Consistency is key in diving. If you're consistent, and catching up on someone, and putting the pressure on, they start blowing their dives a little bit. They start to wobble.'

The Chinese are the guys to beat, he says. 'They're the top diving nation. I don't know why. They've dominated for a long time. They train them from the age of five. They're constantly stretching them, trying to get them into shape, and they've got the numbers - diving's the top sport out there. Sometimes I get recognised in China - diving's like the equivalent of football here.' He's been to China three times, so this will be his fourth. 'I'm really looking forward to it. I can't wait to get out there.' And his chances of a medal? 'I don't think it'll happen this time. I'm not expecting anything - I'm just going out there to learn something for 2012.'

Olympic rower and multi-gold-medallist Steve Redgrave - who has been helping to mentor more than a dozen athletes in the past 18 months - describes Tom as 'a huge talent' and 'amazingly mature for such a young guy'. But he says the Olympics are different from any other major event, and having him prepared is crucial. 'Tom loves meeting people. He loves meeting sporting celebrities and having his picture taken. Of course it's great being in the limelight - being asked on Richard & Judy or Superstars. And being so young, Tom has become an icon of the games. But,' he says, 'you can't lose sight of what you're trying to do. Maybe he needs a little more protection. I'm not saying he shouldn't do those things, as long as it's not interfering with his training or schoolwork or performance.'

A few days later, I'm at the John Charles Centre for Sport in Leeds for the Olympic diving trials, hunkered down in the blue plastic seating with my glasses steamed up (it's like Mozambique in here), watching the women doing their turns and twists from the high platform. They're pretty amazing, balancing upside down on the last half-inch of board, motionless for a few seconds before flipping backwards into multiple reverse somersaults and swivelling whatnots, hitting the water like knives. Some skip balletically to the brink before spiralling out into the air; others are barely millimetres from banging their heads on the platform, which from here looks like nothing more than a slab of concrete. The judges, unswayed by the whistles and hollering from the crowd, sit poolside on white highchairs doling out niggardly five-and-a-halves and sixes and sevens. I'd give everybody 10 just for getting up the steps and looking over the edge. It's thrilling to watch. It occurs to me that if you didn't have to land on your head, you wouldn't really need water. Diving is a water sport in the same way that pole vaulting is a mattress sport.

Across the aisle I can see Tom lounging in the front row of the spectators' area with his mum and dad and two brothers. Although he has already qualified, he's doing a display session on the 10-metre platform this afternoon.

The women's preliminaries over, I go down to the café and speak to Tom's personal mentor, Leon Taylor, who won an Olympic silver in 2004. Leon had been hoping to compete in Beijing himself but had to retire through injury. He's 30 - that's 22 years of hitting the water at 40mph, he says, with its catalogue of shoulder surgery, hernia repairs, overworked joints, and lately a back complaint. 'When your body's had enough, it's had enough.'

Leon met Tom four years ago and offered his services. 'I had no guidelines, but I thought: if I was 10, what would I have benefited from? I've had all this experience, so I just drip-feed it to him - not just about diving, but how he's getting on at school and handling media stuff. In the early days it's quite daunting having a microphone in front of you and an adult questioning you. But, boy, has he accelerated since then - when he was 10 he was beating 17-year-olds; at 13 he was men's European champion. Now he's presenting Baftas!'

What was his best advice for Tom? 'The advice I gave him right at the start: remember, you're doing this because you love it. Regardless of what happens - the times when you don't feel like training, or when competitions go badly - it's not for the fame or the money or the glamour, it's because you love it.'

Tom's partner Blake Aldridge is here, too, nursing a poorly elbow after being shunted off his motorbike by a car on the M25. Now the wound is infected, so he can't dive this afternoon, though he'll be mended in time for Beijing. His bike got wrecked, but his sponsor Apogee ('the office solutions people') went out and bought him a car to get down from Southampton, where he lives and trains and works (at B&Q), to Plymouth for synchro practice with Tom. That's what I call a sponsor.

I ask how the pair of them got together in the first place. It seems slightly odd, what with Blake being 25 and Tom only 14. Blake tells me they were matched up by their coaches. 'I figured, this kid's only going to get better. So we tried it out. Tom didn't have the dives he's got now. But within the space of five months we managed to become number three in the world, number one in Britain, win the world series and qualify for Beijing. It's just a fantastic story, really. And we get on so well in and out of the pool. I've never had a little brother and he's never had a big brother, so it's that sort of scenario.'

I would have thought, too, that the size difference (Blake, 5ft 7in, is four inches taller than Tom, and a lot heavier) might have made synchronisation more difficult, but no. 'We have the same sort of technique, and we look very similar when we're diving; plus we spin at the same speed and jump at the same height. He's a little bit smaller and I'm a little bit stronger, so he spins a little bit faster and I spin a little bit slower, so the strength and the size meet each other.'

I nod. It sounds plausible. But are they up for a medal?

'Our mindset is just to get in there and put on a good performance. I always say to Tom: let's just get in there and do what we do, and the results will take care of themselves. For me, the hard work was qualifying for the Olympics. It'll be a bonus if we walk away with a medal.'

I go back to the gallery to watch Tom go through his 'list', his set of six dives for Beijing. It's true he doesn't jump very high, but his reverse triple somersault is crisp and measured. Then back he goes, tossing his twist of towel into the water, then standing up there, taut in his small-man's body, his eyes fixed on something only he can see... then off he tumbles again, folding and unfolding in a whir of neatness. The judges, though ostensibly unimpressed, give him nines, nine-and-a-halves, and a 10. Even they secretly love him.

Today has a celebratory feel, but afterwards I ask him how it is in the heat of competition, going up those steps. 'I run up them. I can't wait to get up there. I do get nervous but excited at the same time. It's quite weird. But you just try to compose yourself and try and use the adrenaline in your favour.'

What sort of mental training is involved? 'We do visualisation, shut our eyes and watch it in our head, as if we were doing it, so we know what to expect when we get on to the board.'

And do you have time to think about it? 'It's unbelievable, really. It's only 2.2 seconds, but when you do it, it feels like you're going in slow motion, and it feels like you've got loads of time. When you're spinning round, you're thinking: I'm slightly too high... but then with your body instincts you can make minor adjustments to make yourself land on your head. It's surprising how much time you've got.'

Tom's vitality and glow remind me that in another way, of course, time has a habit of whizzing by for sports-people, whose careers span an artificially elongated youth. On the way to the stadium, I found myself asking for directions in a pub in one of the grimier precincts of newly gentrified Leeds where the landlord turned out to be the Seventies Leeds United striker Peter 'Hot Shot' Lorimer, a boyhood idol of my own. I shook his hand, we chatted for a minute and, naturally, he was able to point me towards the John Charles Centre for Sport - named in honour of an earlier Leeds (and Juventus) footballing great. Charles, too, had done time in the licensing trade. Going into pub work wasn't an unusual second career for sportsmen of that generation, but on this day in 2008 - the air here charged with positive mental attitude - it seems slightly dispiriting.

I ask Tom what he'll do when his own spring finally goes. 'I'd like maybe to go into TV presenting or sports reporting, or children's TV - something like that.'

I can imagine that. And, of course, such ambitions are better accommodated these days. Leon, crocked at 30, is easing himself into media work with the BBC's 'Talent' programme. He works with schools, too, and does corporate teambuilding and motivational speaking. Even the young woman from Radio 5 Live sitting next to me in the media enclosure turns out to be an ex-Olympic swimmer - Karen Pickering, from Ipswich. She says she's 36, but looks like a PE student. (I Google her later to find she has hundreds of medals, including an MBE.) She answers my dumb questions about synchro (yes, they have to hit the water at the same time) and how the scoring works. Do you get points for wearing matching swimsuits? No, she says. We sit through the springboard and platform finals, and watch the competitors introduced by girls in Chinese costume. The judges, impassive, give out scores - higher ones now.

Afterwards I speak to Tom's coach, Andy Banks, who sees Tom six days a week. I ask if there is such a thing as natural talent. Absolutely, he says, 'and Tom has it in oodles', though when he first saw Tom 'he just sat on the poolside and cried the whole time. He was about eight. I never thought he'd make a diver. He was scared of a dive and didn't want to get in. But when I managed to get him in the water I could see he had talent.'

Tom's road to Beijing started three years ago, says Andy. 'I thought there was an outside chance of 2008. We had a plan, in terms of when he learnt the dives, how fast we progressed him, what competitions he should do. We thought it was just possible to get him there. But he outgrew that plan. The milestones I had in place - he got to them before he was supposed to.'

Andy answers with some weariness when I bring up the question of medals: 'The media are always after the medal thing. Medals aren't a goal this time. The goal is for him to come away happy with his performance and learn as much as he can from the whole environment.'

Yes, yes, of course - but will he get one in 2012? 'Maybe. Hopefully, as he gets bigger and stronger, and then... but then it depends on whether he grows too much - it doesn't help if you're too tall. But so far so good - he's developed the weight along with the height, the body line is good, and he can still spin as quickly as he needs to.'

Back at the poolside, the 10 qualifiers, happily damp and tousled and tracksuited, are paraded for the closing ceremony, raising their prize bouquets to the whistles of the crowd. Tom gets the biggest cheer.

I admire but also slightly fear for him - as you might for anyone who sees a light to follow so perilously early in life. Doubtless I'd have felt the same about Mozart ('For goodness sake, go outside and get some fresh air, Amadeus!'). I suppose the thing is, while some competitive sports seem like an extension of fun - or at least recognisable as something you might do yourself in a more half-arsed way - diving is one of those that has escaped the compass of everyday experience. For the general ignoramus, the Olympics are the opening of a great zoo of such diverse sporting exotica, characterised by the unknowable minutiae of their conventions and their demands for solitude, sacrifice and pain.

But if it seems strange to devote your life so particularly to doing this one thing better than anyone else, it seems less strange on occasions like this, when singular people become less so by being banded together for the afternoon. I watch Tom down there bonding with his fellows, his dad filming from the gallery above, inspirational music booming out now. Seeing him with the others, their arms round each other in a communal hug, gleeful in their matching Olympic livery, he doesn't seem so different. Rather, they all look like kids - even those who have been here before - at the start of a big adventure.